Sleep sack



FIG. 1 is a front perspective view of a sleep sack;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a back elevational view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is a top perspective view of the sleep sack in use.

The broken lines in the drawings are included for the purpose of illustrating environment and form no part of the claimed design. The stippling shown within the drawing disclosure represents contrast in materials that forms part of the claimed design. 

CLAIM The ornamental design for a sleep sack, as shown and described. 